Substrates of aluminium or aluminium alloy in the form of sheet or extrusion, are used to make shaped or formed products. In some of these processes parts of (shaped) aluminium comprising substrates are interconnected. One end of a substrate may be interconnected with the other end or one substrate may be assembled with one or more other substrates. This is commonly done by brazing, a technique well known to the person skilled in the art. In a brazing process, a brazing filler metal or brazing alloy, or a composition producing a brazing alloy upon heating, is applied to at least one portion of the substrate to be brazed. After the substrate parts are assembled, they are heated until the brazing metal or brazing alloy melts. The melting point of the brazing material is lower than the melting point of the aluminium substrate or aluminium core sheet.
Brazing sheet products find wide applications in heat exchangers and other similar equipment. Conventional brazing products have a core of rolled sheet, typically, but not exclusively an aluminium alloy of the 3xxx-series, having on at least one surface of the core sheet an aluminium brazing clad layer. The aluminium brazing clad layer is commonly made of a 4xxx-series alloy comprising silicon in an amount in the range of 2% to 20% by weight, and preferably in the range of about 7% to 14% by weight. The aluminium brazing clad layer may be coupled or bonded to the core alloy in various ways known in the art, for example by means of roll bonding, cladding spray-forming or semi-continuous or continuous casting processes. These aluminium brazing clad layers have a liquidus temperature typically in the range of about 540° C. to 615° C.
There is a need for a further improved brazing sheet material that is sufficiently formable to produce complex shaped aluminium substrates and that can be exposed to both vacuum brazing and controlled-atmosphere brazing (“CAB”) events, and achieves high levels of post-braze strength.